This disclosure relates, in various exemplary embodiments, to polycarbonate compositions and articles formed from such compositions having little to no halogen content, and improved fire-retardance and/or drip-resistant characteristics, as well as uses thereof.
With their strength and clarity, polycarbonate (PC) resins have a great many significant commercial applications Unfortunately, polycarbonate resins are inherently not very flame resistant and hence, when burning, can drip hot molten material causing nearby substances to catch fire as well. Thus, in order to safely utilize polycarbonates in many commercial applications, it is necessary to include additives which further retard the flammability of the material and/or which reduce dripping.
A variety of different materials have been described for use in producing fire-retardance (FR) and/or drip-resistant polycarbonates. Examples of these materials include those described in U.S. Pat. Nos. 3,971,756; 4,028,297; 4,110,299; 4,130,530; 4,303,575; 4,335,038; 4,552,911; 4,916,194; 5,218,027; and, 5,508,323.
Flame retardance additives utilized today typically include various sulfonate salts, phosphorous acid esters, brominated and/or chlorinated flame retardants, etc. However, the phosphate additives, which are used at relatively high loadings (i.e. greater than 5 percent, and around 10 percent to produce similar UL94 V0 performance), will deteriorate overall material mechanical performance. Additionally, brominated and chlorinated additives, and even some fluorinated additives at certain loadings, are prohibited by various Non-Government Organizations (NGO's) and environmental protection rules, such as Blue Angel, TCO'99, DIN/VDE, etc. Consequently, sulfonate salts are very widely used today as flame retardance additives.
Examples of sulfonate salt flame retardance additives include perfluoroalkane sulfonates, such as potassium perfluorobutane sulfonate (“KPFBS”, also known as “Rimar salt”). Another sulfonate salt flame retardance additive is, for example, potassium diphenylsulfone sulfonate (“KSS”).
In this regard, the use of perfluoroalkane sulfonates in polycarbonate resins is described in U.S. Pat. No. 3,775,367. Additionally, U.S. Pat. No. 6,353,046 discloses that improved fire properties can be imparted to polycarbonate resin compositions by incorporating into the polycarbonate, potassium perfluorobutane sulfonate, and a cyclic siloxane, such as octaphenylcyclotetrasiloxane. U.S. Pat. No. 6,790,899 specifies the finding of a synergistic effect between KPFBS and sodium salt of toluene sulfonic acid (NaTS) on flame retardant polycarbonate compositions. Moreover, U.S. Patent Application 20050009968 teaches the synergistic effect between KPFBS and a number of inorganic sodium salts in transparent flame retardant carbonate compositions. Nevertheless, KPFBS contains fluorine and therefore is not Blue Angel conforming.
When thinner wall flame retardant performance is desired, a fluoro-containing anti-dripping additive may be utilized. However, to meet the Eco label requirements, only limited loading of the fluoro-containing anti-dripping additive can be used. For example, DIN/VDE requires a fluorine content of no more than 0.1 percent. However, the anti-dripping effect with this limited amount of fluoro-containing anti-dripping additive is generally poor. For example, when using a KSS/NaTS combination as the flame retardant package and TSAN as the anti-dripping additive at the DIN/VDE required loading, one cannot obtain a polycarbonate composition exhibiting a UL94 V0 @ 1.5 mm rating.
Furthermore, only limited fire-retardance performance can be obtained when KSS is used alone. The conventional means for enhancing the fire-retardancy properties while retaining transparency has been through the use of soluble organic halogen additives with KSS. For example, in some polycarbonate resin compositions, KSS with a loading of 0.3-0.5 phr is used with brominated polycarbonate. Without the bromine, those compositions have inconsistent/unreliable performance in the UL94 V0 @ 3.0 mm flammability test that these compositions are designed to meet.
There accordingly remains a need in the art for polycarbonate compositions containing minimal or no halogen that can readily produce an article with improved fire-retardance and/or drip-resistant characteristics, among others.